Golf ball

ABSTRACT

A golf ball with a center and a cover layer formed over the center is disclosed. The center exhibits a high velocity and is soft with a compression of less than about 75. The cover layer is soft with a Shore D hardness on the ball of less than about 58. The cover layer includes an ionomer component and a metallocene polymer component. The ionomer component can be a single ionomer or a blend of ionomers. The metallocene polymer component can be a single metallocene polymer or a blend of metallocene polymers.

FIELD OF THE INVENTION

[0001] The present invention relates to golf balls and moreparticularly, the invention is directed to improved golf balls includinga soft, high-velocity core and a surrounding soft cover layer comprisingan ionomer component and a metallocene polymer component.

BACKGROUND OF THE INVENTION

[0002] Conventional golf balls can be divided into two general types orgroups: solid balls or wound balls. The difference in playcharacteristics resulting from these different constructions can bequite significant. These balls, however, have primarily two functionalcomponents that make them work. These components are the center or coreand the cover. The primary purpose of the core is to be the “engine” ofthe ball or the principal source of resiliency. The primary purpose ofthe cover is to protect the core.

[0003] Two-piece solid balls are made with a single-solid core, usuallymade of a crosslinked polybutadiene or rubber, which is encased by acover material. These balls are typically the least expensive tomanufacture as the number of components is low and these components canbe formed by relatively quick, automated molding techniques. In theseballs, the solid core is the “engine” or source of resiliency. Theresiliency of the core can be increased by increasing the crosslinkdensity of the core material. As the resiliency increases, however, thecompression also increases making a harder ball, which is undesirable.

[0004] Polybutadiene cores in solid balls are adversely affected bymoisture, and to protect against moisture their covers should have goodmoisture barrier properties and should be applied to the cores soonafter their formation. One way to achieve a desirable golf ball is tocover a high-velocity polybutadiene core with a urethane cover. Thistype of golf ball exhibits low driver spin and high velocity fordistance with high half-wedge spin for control around the greens. Sinceurethane lacks optimal moisture barrier properties, a polybutadiene coreof such a two-piece ball, however, can lose its high velocity quickly,which is undesirable. As a result, balls with polybutadiene cores andurethane covers may include an intermediate layer for moisture control.

[0005] High velocity cores have also been covered with blends of lowmodulus ionomers, which offer better moisture barrier properties thanurethane. These covers, however, lack resiliency so that the desiredball velocity is not achieved.

[0006] Hence, there remains a need for a two-piece ball design thatprovides a soft, high-velocity core and a surrounding soft cover layerfor low driver spin with high velocity and high half-wedge spin whilealso having good moisture barrier characteristics.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a two-piece golf ball with acenter and at least one cover layer surrounding the center. Theinventive golf ball provides low driver spin and high velocity with highhalf-wedge spin. The inventive gall also exhibits good moisture barriercharacteristics.

[0008] According to one embodiment of the present invention, the golfball includes a soft center and a soft cover layer. The center has acompression of less than about 75. More preferably, the compression ofthe center is between about 63 and about 73. The cover layer has a ShoreD hardness less than about 58 on the ball. Preferably, the cover layeris formed of an ionomer component and a metallocene polymer component.The ionomer component can be a single ionomer or a blend of ionomers.The metallocene polymer component can be a single metallocene polymer ora blend of such polymers.

[0009] According to one aspect of the present invention, the center hasa diameter greater than about 1.50 inches. More preferably, the centerhas a diameter between about 1.55 inches and about 1.60 inches.

[0010] According to another aspect of the present invention, the coverlayer has a Shore D hardness on the ball of less than about 55. Morepreferably, the cover layer has a Shore D hardness on the ball ofbetween about 50 and about 52.

[0011] According to another feature of the present invention, the coverlayer includes about 50% to about 70% of the ionomer component and about50% to about 30% of the metallocene polymer component. More preferably,the cover layer includes about 60% of the ionomer component and about40% of the metallocene polymer component.

[0012] In yet another embodiment, the golf ball comprises the center andat least one cover layer surrounding the center. The center has acompression of about 63. The cover layer is formed of an ionomercomponent and a metallocene polymer component, and the cover layer has aShore D hardness on the ball less than about 58.

[0013] According to one aspect of the present inventive ball, thecompression of the golf ball is greater than about 70. More preferably,the compression of the golf ball is between about 74 and about 80.

[0014] In one embodiment, the center includes polybutadiene, zincdiacrylate, peroxide, a filler, and zinc oxide. In such a ball, thecenter may include a polybutadiene with a Mooney viscosity between about40 and about 60. The center may also include a polybutadiene blend of afirst and second polybutadiene, the first polybutadiene having a Mooneyviscosity between about 30 and about 50 and the second polybutadienehaving a Mooney viscosity between 50 and about 70. If the zincdiacrylate is greater than 30 pph of the polybutadiene, the center mayfurther include organic sulfur. If the zinc diacrylate is less than 30pph of the polybutadiene, the center may omit organic sulfur. The fillermay be a high specific gravity material such as tungsten, bariumsulfate, tungsten trioxide, iron, magnesium, or manganese.

[0015] Another embodiment of the present invention is a two-piece golfball comprising a center with a compression of less than about 75 and asingle cover layer surrounding the center. The cover layer is formed ofa lithium ionomer and a metallocene polymer. The cover layer has a ShoreD hardness less than about 58 on the ball.

[0016] According to one aspect of such a golf ball, the center mayinclude only a single layer. According to another aspect of such a golfhall, the center can be adjacent the cover layer so that the ball doesnot include an intermediate layer between the center and cover layer.

BRIEF DESCRIPTION OF THE DRAWING

[0017] In the accompanying drawing which forms a part of thespecification and is to be read in conjunction therewith:

[0018]FIG. 1 is a cross-sectional view of a two-piece golf ballaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Referring to FIG. 1, golf ball 1 is shown. Golf ball 1 includes acenter 2 surrounded by at least one cover layer 3, which forms the outersurface of the golf ball. Preferably, in the golf ball 1, there is onlya single center 2 and only a single cover layer 3. The cover layer 3 ispreferably formed of a blend of at least one ionomer and at least onemetallocene polymer.

[0020] The center 2 may be of any dimension or composition, so long asit has a compression of less than about 75. More preferably, thecompression of the center is between about 63 and about 73. Thecompression measurement can be obtained using a commercial compressiontester manufactured and sold by ATTI Engineering in New Jersey.Preferably, the center 2 has a diameter greater than about 1.50 inches,more preferably has a diameter between about 1.55 inches and about 1.60inches, and most preferably between about 1.55 inches and about 1.59inches.

[0021] Preferably, the center 2 is formed of a resilient polymer basematerial, such as polybutadiene, natural rubber, polyisoprene,styrene-butadiene, or ethylene-propylene-diene rubber. This basematerial may be combined with other components. A preferred basecomposition for forming the golf ball center 2 prepared in accordancewith the present invention generally comprises polybutadiene and, inparts by weight based on 100 parts polybutadiene, about 22 parts perhundred (pph) to about 35 pph of a metal salt diacrylate,dimethacrylate, or monomethacrylate, preferably zinc diacrylate (ZDA), afree radical initiator, zinc oxide, and filler The polybutadienepreferably has a cis 1,4 content of above about 90% and more preferablyabove about 96%. In addition, the polybutadiene preferably has amid-Mooney viscosity. Mid-Mooney viscosity is between about 40 and about60. Mooney viscosity is typically measured according to ASTM D-1646.

[0022] Commercial sources of useful polybutadiene include CB 23, whichhas a Mooney viscosity of about 51, and is a highly linear polybutadienerubber sold by Bayer. If desired, the polybutadiene can also be mixedwith other elastomers known in the art, such as natural rubber,styrene-butadiene, low Mooney viscosity polybutadiene (i.e., with aMooney viscosity of less than 40) and/or isoprene in order to furthermodify the properties of the center. Preferable low Mooney viscositypolybutadienes include Shell 20 and Ubepol 130B manufactured by Shelland EniChem, respectively. When a mixture of elastomers is used, theamounts of other constituents in the base material are based on 100parts by weight of the total elastomer mixture.

[0023] Metal salt diacrylates, dimethacrylates, and monomethacrylatessuitable for use in this invention include those wherein the metal ismagnesium, calcium, zinc, aluminum, sodium, lithium, zinc, or nickel.ZDA is preferred, but the present invention is not limited thereto. ZDAprovides golf balls with a high initial velocity. The ZDA can be ofvarious grades of purity. For the purposes of this invention, the lowerthe quantity of zinc stearate present in the ZDA the higher the ZDApurity. ZDA containing less than about 10% zinc stearate is preferable.More preferable is ZDA containing between about 4% and about 8% zincstearate. Suitable, commercially available zinc diacrylates includethose from Rockland React-Rite and Sartomer. The preferredconcentrations of ZDA that can be used are about 25 pph to about 35 pphbased upon 100 pph of polybutadiene or alternately, polybutadiene with amixture of other elastomers that equal 100 pph.

[0024] Free radical initiators are used to promote cross-linking of themetal salt diacrylate, dimethacrylate, or monomethacrylate and thepolybutadiene. Suitable free radical initiators for use in the inventioninclude, but are not limited to peroxide compounds, such as dicumylperoxide, 1,1-di (t-butylperoxy) 3,3,5-trimethyl cyclohexane, bis(t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di (t-butylperoxy)hexane, or di-t-butyl peroxide, and mixtures thereof. Other usefulinitiators would be readily apparent to one of ordinary skill in the artwithout any need for undue experimentation. The initiator(s) at betweenabout 70% and about 100% activity are preferably added in an amountranging between about 0.05 pph and about 2.5 pph based upon 100 parts ofbutadiene, or butadiene mixed with one or more other elastomers. Morepreferably, the amount of initiator added ranges between about 0.15 pphand about 2 pph, and most preferably the amount of initiator addedbetween about 0.25 pph and about 1.5 pph. Suitable commerciallyavailable dicumyl peroxides include Perkadox BC, which is a 90% activedicumyl peroxide, and DCP 70, which is a 70% active dicumyl peroxide.The present invention further includes between about 5 pph to about 50pph zinc oxide in the ZDA-peroxide cure system that crosslinks thepolybutadiene during the core molding process.

[0025] When the amount of zinc diacrylate is greater than about 30 pph,then a plasticizer, such as organic sulfur can be added to the centercomposition. On the other hand, when the amount of zinc diacrylate isless than about 30 pph, then the composition may omit the plasticizer ororganic sulfur. In accordance to another aspect of the invention, theaddition of an organic sulfur compound to the center further increasesthe resiliency and the coefficient of restitution of the ball even atlow compressions. Preferred organic sulfur compounds include, but arenot limited to, pentachlorothiophenol (“PCTP”) and a salt of PCTP. Apreferred salt of PCTP is ZnPCTP. The utilization of PCTP and ZnPCTP ingolf ball cores to produce soft and fast cores is disclosed inco-pending U.S. application Ser. No. 09/951,963 filed on Sep. 13, 2001,and is assigned to the same assignee as the present invention. Thisco-pending application is incorporated by reference herein, in itsentirety. A suitable PCTP is sold by the Struktol Company under thetradename A95. ZnPCTP is commercially available from EchinaChem.

[0026] The center compositions of the present invention preferablyinclude fillers, added to the elastomeric composition to adjust thedensity and/or specific gravity of the center. As used herein, the term“fillers” includes any compound or composition that can be used to varythe density and other properties of the subject golf ball core.Appropriate filters preferably used range in specific gravity from about5 to about 19, preferably from about 2 to about 5.6. Fillers useful inthe golf ball core according to the present invention include, forexample, metal (or metal alloy) powders, metal oxide, metal stearates,particulate, carbonaceous materials, and the like or blends thereof. Theamount and type of filler utilized is governed by the amount and weightof other ingredients in the composition, since a maximum golf ballweight of 1.620 ounces has been established by the United States GolfAssociation (“USGA”).

[0027] Examples of useful metal (or metal alloy) powders include, butare not limited to, bismuth powder, boron powder, brass powder, bronzepowder, cobalt powder, copper powder, inconel metal powder, iron metalpowder, molybdenum powder, nickel powder, stainless steel powder,titanium metal powder, zirconium oxide powder, aluminum flakes, tungstenmetal powder, beryllium metal powder, zinc metal powder, or tin metalpowder. Examples of metal oxides include but are not limited to zincoxide, iron oxide, aluminum oxide, titanium dioxide, magnesium oxide,zirconium oxide, and tungsten trioxide. Examples of particulatecarbonaceous materials include but are not limited to graphite andcarbon black. Examples of other useful fillers include but are notlimited to graphite fibers, precipitated hydrated silica, clay, talc,glass fibers, aramid fibers, mica, calcium metasilicate, barium sulfate,zinc sulfide, silicates, diatomaceous earth, calcium carbonate,magnesium carbonate, regrind (which is recycled uncured center materialmixed and ground to 30 mesh particle size), manganese powder, andmagnesium powder.

[0028] Antioxidants may also be included in the elastomeric centersproduced according to the present invention. Antioxidants are compoundsthat prevent the breakdown of the elastomer. Antioxidants useful in thepresent invention include, but are not limited to, quinoline typeantioxidants, amine type antioxidants, and phenolic type antioxidants.

[0029] Other ingredients such as accelerators, e.g. tetra methylthiuram,processing aids, processing oils, dyes and pigments, as well as otheradditives well known to one of ordinary skill in the art may also beused in the present invention in amounts sufficient to achieve thepurpose for which they are typically used.

[0030] The center 2 may be formed by mixing and forming the basecomposition using conventional techniques. More particularly, the centercompositions of the invention are produced by forming a mixturecomprising polybutadiene, zinc diacrylate, the plasticizer, if used,zinc oxide, and filler. When a set of predetermined conditions is met,i.e., time and temperature of mixing, the free radical initiator isadded. In particular, as the components are mixed, the resultant shearcauses the temperature of the mixture to rise.

[0031] After completion of the mixing, the golf ball center compositionis milled and hand prepped or extruded using a machine into pieces(“preps”) suitable for molding. The milled preps are then compressionmolded into centers at an elevated temperature. Typically, about 160° C.(320° F.) for approximately 15 minutes at about 2000 psi is suitable formolding the center. These centers can then be used to make finished golfballs by surrounding the centers with cover materials.

[0032] Referring to FIG. 1, the cover layer 3 can be formed with aplurality of dimples (not shown) defined thereon. Preferably, thethickness of the cover layer is between about 0.020 inches and about0.07 inches, more preferably between about 0.03 inches and about 0.065inches, and most preferablt between about 0.045 inches and about 0.065inches. In addition, the preferred cover layer 3 is formed of a blend ofat least one ionomer resin and one or more metallocene polymers suchthat the cover layer has a Shore D hardness on the ball of less thanabout 60 and greater than about 48. More preferably, the Shore Dhardness on the ball is less than about 58, and most preferably theShore D hardness of the cover material on the ball is between about 50and about 52. If the cover material is measured prior to placement onthe center, it is in a slab, and Shore D hardness off the ball ispreferably less than about 50. More preferably, the Shore D hardness offthe ball is between about 42 and about 48. Shore D hardness off the ballis measured in accordance with ASTM D 2240-86 durometer hardness.

[0033] In such a cover layer, preferably, the ionomer or ionomer blendforms an ionomer component that is between about 50% and about 70% ofthe cover material. Preferably, the metallocene polymer or blend of suchpolymers forms a metallocene polymer component that is between about 50%and about 30% of the cover material. More preferably, the ionomercomponent forms about 60% of the cover material and the metallocenepolymer component forms about 40% of the cover material. According toone aspect of the present invention, the ionomer component can be formedof a single ionomer or blend of ionomers and similarly the metallocenecomponent can be formed of a single metallocene polymer or a blend ofmetallocene polymers in various combinations. Advantageously, theionomer-metallocene blend used for the cover exhibits a lower watervapor transmission rate than a thermoset urethane material. The typicalWater Vapor Transmission Rate (“WVTR”) values for some ionomer and someurethane materials are about 0.2870 g/100 in²-day and about 12.62 g/100in²-day, respectively. Each WVTR is measured at 37.8° C. and 100%relative humidity.

[0034] Exemplary ionomers useful in the inventive ball are ethylenemethacrylic acid ionomers, and ethylene acrylic acid ionomers, and theirterpolymers, currently sold commercially under the trade names SURLYN®and IOTEK® by DuPont and Exxon, respectively. These and other polymersand ionomers are described in U.S. Pat. No. 5,155,157 and CanadianPatent No. 963,380. Other polymers which can be used in conjunction withthe ethylene metallocene catalyzed polymers of the claimed invention ingolf ball covers include: poly(ethylethylene), poly(heptylethylene),poly(hexyldecylethylene), poly(isopentylethylene),poly(1,1-dimethyltrimethylene), poly(1,1,2-trimethyltrimethylene),poly(butyl acrylate), poly(4-cyanobutyl acrylate), poly(2-ethylbutylacrylate), poly(heptyl acrylate), poly(2-methylbutyl acrylate),poly(3-methylbutyl acrylate), poly(N-octadecylacrylarnide),poly(octadecyl methacrylate), poly(butoxyethylene),poly-1,1-bis(trifluoromethoxy)difluoroethylene, poly(methoxyethylene),poly(pentyloxyethylene), poly(1,1-dichloroethylene),poly(cyclopentylacetoxyethylene),poly(4-(2-butoxyethoxy)methyl-styrene), poly(4-dodecylstyrene),poly(4-tetradecylstyrene), poly(phenetylmethylethylene),polyoxy(allyloxymethyl)ethylene, polyoxy(ethoxymethyl)ethylene,poly(oxyethylethylene), poly(oxytetramethylene), poly(oxytrimethylene),poly(oxycarbonylpentamethylene),poly(oxycarbonyl-3-methylpentamethylene),poly(oxycarbonyl-1,5-dimethylpentamethylene),poly(oxy-2,2,3,3,4,4-hexafluoropentamethyleneoxyadipoyl),polyoxy(methyl)-3,3,3-trifluoropropylsilylene-3,3-difluoropentamethylene(methyl)-3,3,3-trifluoropropylsilylene,poly(silanes) and poly(silazanes), main-chain heterocyclic polymers andpoly(furan tetracarboxylic acid diimides) as well as the classes ofpolymers to which they belong.

[0035] Preferably, the ionomer is selected from a group of ionomersincluding sodium, lithium, zinc or magnesium ionomer resins or blendsthereof. Such blends can include two of the above ionomer resins or allthree ionomer resins. In a preferred embodiment, the ionomer componentis a thermoplastic, lithium ionomer resin, such as SURLYN®, which iscommercially available from DuPont. The preferred golf ball compositionscomprise one or more ionomer resins having a flexural modulus of fromabout 50 psi to about 150,000 psi and a non-ionic metallocene catalyzedcopolymer of an olefin having a flexural modulus of from about 500 psito 200,000 psi. Flexural modulus is measured according to ASTM 6272-98.The test specimen should be conditioned for a period of at least twoweeks.

[0036] As used herein, the term “metallocene polymer” refers to anypolymer, copolymer, or terpolymer useful in the present invention thatis formed using metallocene catalyst technology. Preferably, themetallocene catalyzed polymers have the formula:

[0037] wherein R₁ is hydrogen, branched or straight chain alkyl such asmethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl,carbocyclic, aromatic or heterocyclic;

[0038] R₂ is hydrogen, lower alkyl including C₁-C_(5;)

[0039] carbocyclic, aromatic or heterocyclic

[0040] R₃ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic;

[0041] R₄ is selected from the group consisting of C_(n)H_(2n+1), forn=1 to 18 (which includes CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁1, C₆H₁₃, C₇H₁₅,C₈H₁₇, C₉H₁₉, C₁₀H₂₁) and phenyl, in which from 0 to 5H within R₄ can bereplaced by substituents selected from the group consisting of COOH,SO₃H, NH₂, F, Cl, Br, I, OH, SH, silicone, lower alkyl esters and loweralkyl ethers, with the proviso that R₃ and R₄ an be combined to form abicyclic ring;

[0042] R₅ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic,

[0043] R₆ is hydrogen, lower alkyl including C₁-C₅, carbocyclic,aromatic or heterocyclic; and wherein x, y and z are the relativepercentages of each co-monomer. The number x can range from 1-99 percentor more preferably from 10-70 percent and most preferred, from about10-50 percent. The number y can be from 99-1 percent, preferably, from90-30 percent, or most preferably, 90-50 percent. The number z can rangefrom 0 to 49 percent, as disclosed in U.S. Pat. No. 5,703,166incorporated herein by reference in its entirety.

[0044] Residual metallocene catalyst may also be present in the subjectcomposition as these catalysts are used in the manufacture of themetallocene catalyzed co-polymers that are useful in the golf ball covercompositions of the present inventive ball.

[0045] In the preferred metallocene catalyzed copolymer, R₁ is hydrogenor lower alkenyl, R₂ is hydrogen or alkyl, including carbon chainshaving from 1 to 10 carbon atoms, R₃ is hydrogen or lower alkyl oralkenyl such as carbon chains having 1-10 carbon atoms, and R₄ is alower alkyl group having from 1-10 carbon atoms. For terpolymers, wherez is not zero, R₅ is preferably hydrogen or lower alkyl or alkenyl suchas carbon chains having 1-10 carbon atoms, and R₆ is a lower alkyl grouphaving from 1-10 carbon atoms. In the most preferred copolymer, R₁ andR₂ are hydrogen, R₃ is hydrogen, methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl or octyl, and R₄ is a straight carbon chain having 6carbon atoms. For terpolymers, R₅ is most preferably hydrogen, methyl,ethyl, propyl, butyl, pentyl, hexyl, heptyl or octyl, and R₆ is astraight carbon chain having 6 carbon atoms.

[0046] The subject metallocene catalyzed copolymers can be random orblock copolymers and may be made by blending two, three, four, five ormore different monomers according to processes well known to one ofordinary skill in the art. Additionally, the subject metallocenecatalyzed polymers may be isotactic, syndotactic or atactic, or anycombination of these forms of types of polymers. The pendant groupscreating the isotactic, syndotactic or atactic polymers are chosen todetermine the interactions between the different polymer chains makingup the resin to control the final properties of the resins used in golfball covers. Aromatic and cyclic olefins can be used in the presentinvention as well as such specific groups as methyl and phenyl.

[0047] As used herein, the phrase linear chain or branched chained alkylgroups of up to about 30 carbon atoms means any substituted orunsubstituted acyclic carbon-containing compounds, including alkanes,alkenes and alkynes. Examples of alkyl groups include lower alkyl, forexample, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl ortert-butyl; upper alkyl, for example, octyl, nonyl, decyl, and the like;and lower alkylene, for example, ethylene, propylene, propyldiene,butylene, butyldiene, pentene, hexene, heptene, octene, norbomene,nonene, decene and the like. The ordinary skilled artisan is familiarwith numerous linear and branched alkyl groups, which are within thescope of the present invention.

[0048] In addition, such alkyl group may also contain varioussubstituents in which one or more hydrogen atoms has been replaced by afunctional group. Functional groups include but are not limited tohydroxyl, amino, carboxyl, sulfonic amide, ester, ether, phosphates,thiol, nitro, silane and halogen (fluorine, chlorine, bromine andiodine), to mention but a few.

[0049] As used herein, substituted and unsubstituted carbocyclic groupsof up to about 20 carbon atoms means cyclic carbon-containing compounds,including but not limited to cyclopentyl, cyclohexyl, cycloheptyl,adamantyl, and the like. Such cyclic groups may also contain varioussubstituents in which one or more hydrogen atoms has been replaced by afunctional group. Such functional groups include those described above,and lower alkyl groups having from 1-28 carbon atoms. The cyclic groupsof the invention may further comprise a heteroatom. For example, in aspecific embodiment, R₂ is cyclohexanol.

[0050] As used herein, substituted and unsubstituted aryl groups means ahydrocarbon ring bearing a system of conjugated double bonds, usuallycomprising six or more even number of π electrons. Examples of arylgroups include, but are not limited to phenyl, naphthyl, anisyl, toluyl,xylenyl and the like. According to the present invention, aryl alsoincludes heteroaryl groups, e.g., pyrimidine or thiophene. These arylgroups may also be substituted with any number of a variety offunctional groups. In addition to the functional groups described abovein connection with substituted alkyl groups and carbocyclic groups,functional groups on the aryl groups can include nitro groups.

[0051] As mentioned above, R₁ and R₂ can also represent any combinationof alkyl, carbocyclic or aryl groups, for example, 1-cyclohexylpropyl,benzyl cyclohexylmethyl, 2-cyclohexylpropyl, 2,2-methylcyclohexylpropyl,2,2-methylphenylpropyl, 2,2-methylphenylbutyl.

[0052] The metallocene catalyzed copolymers useful in the presentinvention are commercially available under the trade name AFFINITY®polyolefin plastomers and ENGAGE® polyolefin elastomers by Dow PlasticsCompany and they are described more fully in U.S. Pat. Nos. 5,272,236and 5,278,272 which are herein incorporated by reference in theirentirety. Other commercially available metallocene catalyzed polymerscan be used such as Exxon's EXACT® and Dow's Insight® line of resinswhich have superior flexibility and clarity as well as toughness. TheExact® and Insight® line of polymers also have novel rheologicalbehavior in addition to their other properties as a result of using ametallocene catalyst technology. The method of making EXACT® andINSIGHT® polymers and their compositions are more fully detailed in U.S.Pat. Nos. 5,359,015 and 5,281,679.

[0053] Other polymers may also be used for cover material in golf ballsaccording to the present invention. In particular, any of the polymersthat are disclosed in U.S. Pat. Nos. 2,924,593, 5,055,438 and 5,324,800may be used in golf balls according to the subject invention.

[0054] Further components may also be added to the blended covermaterial, such as, for example; coloring agents, reaction enhancers,crosslinking agents, dyes, lubricants, fillers, excipients, process aidsand other compounds commonly added to polymeric materials and/or golfball covers.

[0055] The golf ball cover compositions of metallocene catalyzedpolymer(s) blended with the ionomer(s) are formed according to blendingmethods well known by those of ordinary skill in the art in aconventional manner using conventional equipment. Good results have beenobtained by mixing the metallocene catalyzed polymer(s) and ionomerresin(s) in a solid, pelletized form and then placing the mix into ahopper which is used to feed the heated barrel of an injection moldingmachine. Further mixing is accomplished by a screw in the heated barrel.

[0056] The injection molding machine is used either to make preformedhalf-shells for compression molding about the center or for moldingflowable cover stock about center using a retractable-pin mold. Suchmachines are conventional. The preferred method is compression molding.

[0057] Half-shells are made by injection molding cover stock into aconventional half-shell mold in a conventional manner. The preformedhalf-shells are then placed about the center and the assembly isintroduced into a compression molding machine. The compression moldingmachine is a hydraulic press having an upper and lower mold plate. Astaught by U.S. Pat. No. 4,508,309 issued Apr. 2, 1985, such mold plateshave half molds, each of which is registered with another half mold inthe opposite mold plate. It has been found that a golf ball is formed inaccordance with the present invention with a cover layer, when thehalf-shells are compression molded about the center at about 250° to400° F. The molded balls are then cooled while still in the mold andfinally removed when the cover layer is hard enough to be handledwithout deforming. After the balls have been molded, they undergovarious conventional finishing operations such as buffing, painting andstamping.

[0058] The present invention can be used with golf balls of any size.While USGA specifications limit the size of a competition golf ball tomore than 1.68 inches in diameter, golf balls of any size can be usedfor leisure golf play. The preferred diameter of the inventive golfballs is from about 1.68 inches to about 1.80 inches. The more preferreddiameter is from about 1.68 inches to about 1.76 inches. A diameter offrom about 1.68 inches to about 1.74 inches is most preferred, howeverdiameters anywhere in the range of from 1.70 to about 1.95 inches can beused. Oversize golf balls above about 1.76 inches to golf balls havingdiameters as big 2.75 inches are also within the scope of the presentinvention.

[0059] These and other aspects of the present invention may be morefully understood by reference to the following examples. While theseexamples are meant to be illustrative of golf balls made according tothe present invention, the present invention is not meant to be limitedby the following examples. TABLE I Inventive Center Inventive CenterIngredient(s) Ex. 1 Ex. 2 Polybutadiene (pph) 100 100 ZDA (pph) 25.5 32Peroxide (pph) 0.5 0.8 Organic Sulfur (pph) 0 2.35 Zinc Oxide 5.0 5.0Filler tungsten barium sulfate Compression 73 63

[0060] TABLE I illustrates two inventive center compositions, where thecenter compression is less than 75. The composition of Inventive CenterExample 1 has less than about 30 pph of ZDA and does not contain organicsulfur. The composition of Inventive Center Example 2 has greater thanabout 30 pph ZDA and does include organic sulfur.

[0061] The composition of Inventive Center Example 1 was formed into twoballs as described in TABLE II. After completion of the ball moldingprocess, the balls are buffed, sand blasted and painted for evaluation.Compression, velocity, and spin tests are performed on the finishedballs. These results are also shown in TABLE II. TABLE II ComparativeProperty Ball Inventive Ball 1 Inventive Ball 2 Core Composition —Inventive Center Ex. 1 Inventive Center Ex. 1 Cover Composition — Blendof ionomer and Blend of ionomer and metallocene polymer metallocenepolymer Core Size (inches) 1.550 1.560 1.590 Ball Compression 85 77 74Ball velocity (ft/s) 253.7 254.3 254.3 Spin Rate - Std. Driver 3293 32413376 (rpm) Spin Rate - Avg. Driver 3749 3813 3925 (rpm) SpinRate - 8Iron 7686 8041 8280 (rpm) Spin Rate - Half Wedge 7004 7241 7344 (rpm)Ball Speed Launch Angle Back Spin Std Driver 160  9.5° 3000 Avg Driver140 10.5° 3600 8 Iron 115 19° 8200 1/2 Wedge 53 31.5° 6900

[0062] The golf ball of the Comparative Ball is a Pro VI ballmanufactured by Titleist®. The Inventive Balls 1 and 2 have centersformed according to Inventive Center Example 1 in TABLE I. InventiveBalls 1 and 2 have covers formed of blend of 60% of a lithium ionomernamed 7940 manufactured by DuPont and 40% of a metallocene polymer namedNMO 525 D manufactured by Fusabond. The Comparative Ball has desirablecompression, velocity and spin characteristics. The Inventive Balls 1and 2 have compressions, velocities and spin characteristicssubstantially equal to those of the Comparative Ball.

[0063] The Inventive Balls 1 and 2 have compressions of 77 and 74,respectively, compared to the Comparative Ball's compression of 85.Hence, the Inventive Balls are as soft or softer than the ComparativeBall.

[0064] The Inventive Balls 1 and 2 have velocities of 254.3 ft/scompared to the Comparative Ball's velocity of 253.7 ft/s. Thus, theInventive Balls are as fast as the Comparative Ball.

[0065] The Inventive Balls 1 and 2 have spin rates off the standarddriver of 3241 rpm and 3376 rpm, respectively, compared to theComparative Ball's spin rate off the standard driver of 3293 rpm. Hence,the Inventive Balls have substantially as low a spin off the standarddriver as the Comparative Ball.

[0066] The Inventive Balls 1 and 2 have spin rates off the averagedriver of 3813 rpm and 3925 rpm, respectively, compared to theComparative Ball's spin rate off the average driver of 3749 rpm. Thus,the Inventive Balls have low spin off the driver within about 180 rpm ofthe Comparative Ball.

[0067] The Inventive Balls 1 and 2 have spin rates off the 8 iron of8041 rpm and 8280 rpm, respectively, compared to the Comparative Ball'sspin rate off the 8 iron of 7686 rpm. Thus, the Inventive Balls have aspin off the 8 iron as high or higher than that of the Comparative Ball.

[0068] The Inventive Balls 1 and 2 have spin rates off a half wedge of7241 rpm and 7344 rpm, respectively, compared to the Comparative Ball'sspin rate off a half wedge of 7004 rpm. Consequently, the InventiveBalls have a spin off a half wedge as high or higher than that of theComparative Ball.

[0069] As shown above, the Inventive Balls 1 and 2 have goodcharacteristics as they exhibit a high velocity of between about 253ft/s and 256 ft/s, low spin off the standard driver of less than about3400 rpm, and high spin off of the half wedge of between about 6500 rpmand 7500 rpm.

[0070] While various descriptions of the present invention are describedabove, it is understood that the various features of the presentinvention can be used singly or in combination thereof. For example, thegolf ball can include a multi-layer center or cover layer. Where thepresent inventive ball uses a dual layer center or core, the inner andouter cores may be formed of elastomeric blends as discussed previously.Furthermore, preferably the inner core may be significantly softer thanthe outer core, while the complete core is still soft with a compressionof less than about 75. Therefore, this invention is not to be limited tothe specifically preferred embodiments depicted therein.

What is claimed is:
 1. A golf ball comprising: a center having acompression of less than about 75; and at least one cover layersurrounding the center, the cover layer formed of an ionomer componentand a metallocene polymer component, and the cover layer having a ShoreD hardness on the ball of less than about
 58. 2. The golf ball of claim1, wherein the center has a compression of between about 63 and about73.
 3. The golf ball of claim 1, wherein the cover layer has a Shore Dhardness on the ball of less than about
 55. 4. The golf ball of claim 2,wherein the cover layer has a Shore D hardness on the ball of betweenabout 50 and about
 52. 5. The golf ball of claim 1, wherein the coverlayer includes about 50% to about 70% of the ionomer component and about50% to about 30% of the metallocene polymer component.
 6. The golf ballof claim 1, wherein the cover layer includes about 60% of the ionomercomponent and about 40% of the metallocene polymer component.
 7. Thegolf ball of claim 1, wherein the ionomer component is a single ionomer.8. The golf ball of claim 1, wherein the ionomer component includes theionomer selected from the group including: a sodium ionomer, a magnesiumionomer, a zinc ionomer, and a lithium ionomer.
 9. The golf ball ofclaim 8, wherein the ionomer component includes at least two differentionomers.
 10. The golf ball of claim 8, wherein the ionomer componentincludes at least three different ionomers.
 11. The golf ball of claim1, wherein the center has a diameter of greater than about 1.50 inches.12. The golf ball of claim 1, wherein the center has a diameter betweenabout 1.55 inches and 1.60 inches.
 13. The golf ball of claim 1, whereinthe center includes less than about 30 pph zinc diacrylate and omitsorganic sulfur.
 14. The golf ball of claim 1, wherein the centerincludes greater than about 30 pph zinc diacrylate and includes organicsulfur and the salts thereof.
 15. A golf ball comprising: a centerhaving a compression of about 63; and at least one cover layersurrounding the center, the cover layer formed of at least one ionomerand at least one metallocene polymer, and the cover layer having a ShoreD hardness on the ball less than about
 58. 16. The golf ball of claim15, wherein the compression of the golf ball is greater than about 70.17. The golf ball of claim 15, wherein the compression of the golf ballis between about 74 and about
 80. 18. The golf ball of claim 15, whereinthe center includes polybutadiene, zinc diacrylate, a free radicalinitiator, zinc oxide, and a filler.
 19. The golf ball of claim 18,wherein the polybutadiene has a Mooney viscosity between about 40 andabout
 60. 20. The golf ball of claim 18, wherein the polybutadiene is ablend of a first and second polybutadiene, the first polybutadienehaving a Mooney viscosity between about 30 and about 50 and the secondpolybutadiene having a Mooney viscosity between 50 and about
 70. 21. Thegolf ball of claim 18, wherein the filler is selected from the groupconsisting of: metal powder, metal alloy powder, metal oxide, metalstearates, particulate carbonaceous materials, tungsten, barium sulfate,iron, manganese, magnesium, copper, and tungsten trioxide.
 22. Atwo-piece golf ball comprising: a center having a compression of lessthan about 75; and a single cover layer surrounding the center, thecover layer formed of a lithium ionomer and a metallocene polymer, andthe cover layer having a Shore D hardness on the ball of less than about58.